g-C3N4/g-C3N4 Heterojunction as the Sulfur Host for Enhanced Cyclic Stability of Li–S Batteries

Li–S batteries are recognized as one of the most promising energy storage and conversion devices because of the high theoretical energy density and acceptable financial and environmental costs but suffer from sluggish sulfur reduction. Herein, the g-C3N4/g-C3N4 heterojunction is synthesized using two kinds of precursors, aiming to adjust the electron cloud structure of g- C3N4 and the interface adhesion energy. This intimate interface of g-C3N4/g-C3N4 endows a significantly accelerated reaction kinetics and enhanced transportation of ions and electrons. Furthermore, the abundant N element of g-C3N4 allows physical confinement and chemical interactions with lithium polysulfides (LiPSs). As a result, a Li–S cell with a g-C3N4/g-C3N4 heterojunction as the sulfur host provides an initial discharge capacity of 1200 mAh/g at 0.1 C and retains 464 mAh/g after 150 cycles at 1 C. It also exhibits a stable rate capability of 350 mAh/g after 500 cycles at 2 C. This study may provide insights into functionalizing g-C3N4 for application in Li–S batteries.